ingo wrote:
> 
> If, in the scene below, I change the y-axis rotation from 90 to 91 deg.
> POV-Ray mentions "creating bounding slabs" and goes on with that forever. At
> 90 deg it traces in a few seconds.
> 
> What is it that happens here?
> 
> ingo
> 
> ----
> #version 3.1;
> #include "colors.inc"
> global_settings {
>     assumed_gamma 1.0
> }
> 
> light_source {<500,200,-500> rgb 1}
> camera {
>     location  <0.0, 3.0,-20.0>
>     look_at   <0.0, 3.0, 0.0>
>     angle 35
> }
> 
> #macro Spits(n,r)
>   #local l=r*2;
>   #local Tz=0;
>   #while (n >=0)
>     #local ru= (0.5*l)/sin(radians(180/n));
>     #local Count=0;
>     #local Rot=0;
>     #while (Count<=n+1)
>       sphere{
>         <0,0,0>,r
>         translate <(cos(radians(Rot)))*ru,(sin(radians(Rot))*ru),Tz>
>       }
>       #local Rot=Rot+(360/n);
>       #local Count=Count+1;
>     #end
>     #local n=n-3;
>     #local Tz=Tz-0.25;
>   #end
> #end
> 
> object{
>   union{Spits(33,0.2)}
>   rotate<90,90,0>      // Change to rotate<90,91,0>
>   pigment{White}
> }

The only problem I could discover was your line "#while (n >=0)"
followed by "#local ru= (0.5*l)/sin(radians(180/n));".  If n starts as a
multiple of 3, and hence reaches 0, POV-Ray will crash while parsing
when it encounters the attempt to divide 180 by zero.  Changing the
n >=0 to n >0 fixed that problem, after which I had no trouble rendering
with rotate <90, 91, 0> applied to the finished object (on POV-Ray 3.1
and 3.1a for DOS, nor 3.1a for Windows).

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